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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Vol. 53 (2013), No. 9

  • Effect of Surface Properties of Iron Ores on their Granulation Behavior

    pp. 1491-1496

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    DOI:10.2355/isijinternational.53.1491

    The granulation property of iron ores was generally influenced by their wettability, surface roughness and shape of the iron ore. In this study, the surface roughness and shape of iron ores were characterized by the ratio of BET specific surface area (SBET) to specific surface area (SLS) calculated using size distribution obtained by a laser diffraction method. Wettability of ores was characterized by measuring the contact angle (θ) between iron ore and water. Bed permeability was used as an evaluation index of granulation effect. A variety of materials were subjected to a granulation test under an actual production condition. Special attention was paid to four ores with different surface properties and wettabilities. Nine groups of mixtures were obtained by linear programming taking the basicity as the objective function. Granulation results showed that the optimum bed permeability of nine mixtures have a good linear relation with mass fraction of four ores studied. Slopes (k) of fitting lines were used to characterize the granulation properties of ores, binary linear regression equation was derived with the k used as dependent variable, θ and SBET/SLS used as independent variables: k=16.443–0.277×θ+0.058×(SBET/SLS), Granulation performance of iron ore gets better with decreasing the contact angle and increasing the ratio of SBET to SLS.
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    1. Utilization of Biomass for Iron Ore Sintering ISIJ International Vol.53(2013), No.9
    2. Sintering Behavior of Return Fines and their Effective Utilization Method ISIJ International Vol.53(2013), No.9
    3. Effect of Particle Size of Iron Ore and Coke on Granulation Property of Quasi-Particle ISIJ International Vol.53(2013), No.9
  • Technology for Productivity Improvement of Sintering Based on Designing of Composite Granulation and Bed Structure of Sinter Mixture

    pp. 1497-1502

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    DOI:10.2355/isijinternational.53.1497

    Recently, an increase in the amount of fine ore, such as Marra Mamba or Brazilian concentrated ultra fine, in raw material of sinter ore lowers the permeability of sintering bed and the yield of the sinter ore. The collapse of voids in the sintering bed will cause these problems although the bed has a porous structure. Therefore, controlling the bed structure by including loosely packed regions and densely packed regions in the same packed bed has been discussed. This new idea is named MEBIOS (Mosaic Embedding Iron Ore Sintering). In this report, permeability improvement techniques based on MEBIOS concept were studied. In order to granulate large dense green balls with ordinary sinter feed ore, mathematical simulation and granulation tests by using pan pelletizers were carried out. The influence of rim height and pan diameter on movement of raw material in pan was investigated. Also, influence of rim height and slope angle on hold-up and influence of residence time on diameter of green balls were studied. Finally, this technique was installed in Wakayama No. 5 sinter plant. As a result, yearly average productivity of 1.41 t/m2/h and the use of 135 kg/t-sinter Brazilian concentrated ultra fine ore were achieved with 1350 MJ/t-sinter heat consumption for sintering in 2011.
  • Effect of Particle Size of Iron Ore and Coke on Granulation Property of Quasi-Particle

    pp. 1503-1509

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    DOI:10.2355/isijinternational.53.1503

    In order to evaluate quantitatively the distribution of coke breeze in the quasi-particles, the granulation experiment was carried out by using limonite iron ores and coke breeze, and the effects of particle size of iron ore and coke breeze on granulation properties were examined. Moreover, quantitative analysis of coke breeze in a quasi-particle was carried out. The results obtained are follows:
    (1) Regardless of the brand of iron ores and existence of nuclei, the quasi-particle diameter became smaller when coke breeze was added and it became smaller when the particle size of coke breeze became larger. It is thought that the adhesion force by the liquid bridge became smaller because the contact angle between coke and water is larger than that between iron oxide and water.
    (2) The coke contents of P-type quasi-particles without nuclei are almost constant regardless of its diameter because they are equally growing by adhering of the fine iron ore and coke breeze uniformly.
    (3) In case of C-type quasi-particles containing nuclei, the adhering fines layer of C-type quasi-particles is growing by adhering of the fine iron ore and coke breeze uniformly until about 5 mm diameter of it. Consequently, the coke contents in the adhesion fines layer of C-type quasi-particle are almost constant regardless of its diameter. Moreover, it is thought that the peak of carbon content at over 5 mm diameter exists by coalescing of each granule.
  • Continuous Measurement and Control of Sinter Mix Moisture for Decrease in Sintering Fluctuation

    pp. 1510-1514

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    DOI:10.2355/isijinternational.53.1510

    To decrease carbon dioxide emission in iron ore sintering process through reduction of carbon consumption as sintering agent, reduction of fluctuation in iron ore sintering was studied. Transition phenomena of the sintering fluctuation through a sintering plant were observed and studied using a frequency analysis.
    The sintering fluctuation was defined as the cyclic change in the exhaust gas temperatures at a certain wind-box. The observation of the wind box temperatures showed that the temperature changes of several minute cycles existed. To search for upstream causes, charging behavior of the sinter mix to pallet cars was observed using an index of “charging level”. Comparison of the charging level and the wind box temperature showed that the fluctuations of them were almost coincident in the occurring time and position. To search for further upstream causes, a near-infrared moisture meter was introduced to measure sinter mix moisture with high frequency. To investigate the relationship between the wind box temperature, the charging and the sinter mix moisture, a frequency analysis of the fluctuations of them was carried out. It showed that some frequency elements were almost coincident and that fluctuation transferred from the fluctuation in the sinter mix moisture to the sintering.
    Then, a test operation of more precise control of the sinter mix moisture using the near-infrared moisture meters in a sintering plant was carried out. It successfully reduced sintering fluctuation.
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    2. Effect of the Separation of Large Limonite Ore Particles in the Granulation Process of Sinter Raw Materials ISIJ International Vol.53(2013), No.9
    3. Optimization of Dolomite Usage in Iron Ore Sintering Process ISIJ International Vol.53(2013), No.9
  • Optimization of Dolomite Usage in Iron Ore Sintering Process

    pp. 1515-1522

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    DOI:10.2355/isijinternational.53.1515

    To achieve the action mechanism and optimal usage of dolomite in the sintering process, solid reaction tests, fluidity tests, bonding strength tests and sinter pot tests were conducted, then microstructure and energy spectrum were analysed further. Reaction temperature of dolomite with calcium ferrite was lower than that with limonite iron ore about 155°C. Fluidity of bonding phase and strength of sinter using dolomite were lower than that using light burned dolomite and serpentine owing to the higher MgO content in the calcium ferrite and formation of secondary bonding phase. Action mechanism of dolomite in sintering process mainly included 4 steps, thermal decomposition, solid reaction, formation of primary bonding phase and formation of secondary bonding phase. Dolomite mainly played it’s role in the third step in which high viscosity CFM (calcium ferrite with MgO) and magnetite solid solution formed. Increasing the solid solubility of MgO in magnetite by mixing dolomite with magnetite concentrate before granulation, decreasing the dispersity of MgO in sinter mixture by increasing the particle size of dolomite appropriately, increasing the separation degree of MgO and CaO by light-burning the dolomite, and decreasing the reaction amount of MgO by using big particle size magnesia, all could decrease the content of MgO in calcium ferrite, thus showed good performance in sinter pot tests.
  • Effect of Coke Breeze Addition Timing on Sintering Operation

    pp. 1523-1528

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    DOI:10.2355/isijinternational.53.1523

    For the purpose of reducing specific coke breeze consumption, we examined the influence which the morphology of coke breeze and pseudo-particles structure have on sintering quality. As a means to control the morphology of coke breeze in pseudo-particles, we delayed the timing of coke breeze addition in granulation process of sintering materials. As a result, when we added more coke breeze in the latter stage of granulation, we noticed that granulating property as well as permeability were improved. Also, much of coke breeze stayed on the surface layer of pseudo-particles or in free particle, which led to improved quality and burn through speed (abbreviated as BTS).
    When we added the entire charge of coke breeze in the latter stage, combustion quality of coke breeze was improved. However, conduction and accumulation of heat turned down, which resulted in deteriorating yield due to the exhaust heat loss.
    Therefore, we searched for a ratio of the second-stage addition favorable for improving yield by making a higher raw material bed.
    With the second-stage addition at 50%, we were able to build a higher raw material bed through improvement in sinter quality and permeability, while maintaining good BTS. As a result, expanded area in the sintering bed with temperature at 1200°C or higher led to liquid phase growth, which finally enabled the reduction in coke breeze consumption without causing deterioration in both yield and shutter index.
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    3. Influence of CaO Source on the Formation Behavior of Calcium Ferrite in Solid State ISIJ International Vol.53(2013), No.9
  • Effect of the Separation of Large Limonite Ore Particles in the Granulation Process of Sinter Raw Materials

    pp. 1529-1537

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    DOI:10.2355/isijinternational.53.1529

    Sintering with large amount of limonite generally requires higher fuel consumption, either due to the dehydration of combined water or the evaporation of more added water. Although limonite can accelerate melt formation, the sintering strength indexes are in lower level on the contrary, proved to have much to do with the excessive assimilation.
    In order to improve the sintering behavior of sintering mix when large amount of limonite were used, a simplified method named separating large particles of limonite from granulation was investigated by measuring the bonding strength using quasi-particles on the base of confirming influence of excessive assimilation on effective liquid phase of limonite, and calculating changes in properties of sintering mix for moisture transferring. The results obtained were summarized as follows:
    Limonite nuclei adversely influenced bonding strength of quasi-particles mainly by the effective liquid phase, which was determined by volume decrease for penetration and viscosity increment by less fluxed melt, separation of limonite nuclei to reduce the contact interface is helpful in improving bonding of sintered body, and the separation ratio was suggested be within certain range by melt distribution in the whole bed. Less accumulation of condensed water and partial absorption by ungranulated dry limonite resulted in smaller increment in effective mean size and less decrement in void fraction, indicating better bed permeability.
  • Improvement of Permeability of Sintering Bed by Adding Dry Particles to Granulated Raw Materials

    pp. 1538-1544

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    DOI:10.2355/isijinternational.53.1538

    In order to increase the permeability of the sintering bed for sinter ore productivity, RF-MEBIOS (Return Fine - Mosaic Embedding Iron Ore Sintering) process, in which return fine as dry particle is added to granulated raw materials and then they are charged into a sintering machine, is proposed.
    In this paper, the pot suction tests and the direct shear tests were carried out to confirm the reason of increasing permeability of the sintering bed by addition of dry particle. As a result, it is proven that the increasing of permeability is caused by two major phenomena. One is by increasing the pseudo-particle size at granulation and the other is by decreasing the bulk density of the sintering bed after charging. The former is achieved by higher moisture content in the raw materials at granulation. The latter is achieved by higher friction in the packed bed composed of dry and wet particle compounds. Therefore, the voids are easy to remain in the sintering bed when the materials are charged into the sinter machine. The influence of the dry particle brand on permeability is not so strong, but larger dry particles make the permeability higher. Also, when the wet particles are added after granulation, the permeability decreased at the same moisture content condition of the packed bed.
  • Influence of Coke Breeze Positioning on the Sintering Behavior of Pellets and Raw Material Bed with Embedded Pellets

    pp. 1545-1554

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    DOI:10.2355/isijinternational.53.1545

    The influence of coke breeze positioning on the sintering behavior of pellets and raw material bed with embedded pellets was investigated. With increasing the coke breeze ratio in the green pellet made from ore and coke mixture fine of –125 μm, the tensile strength of the green and dried pellets decreased. Based on the evaluations under the green and dried pellet equations concerning particle bond, it was presumed these results were caused by the decrease in the contact points between particles due to the reduction of mixture fine’s specific surface area.
    With increasing the coke breeze ratio in the nucleus pellet, the tensile strength of the burned pellets also decreased. From the change in the porosity up to 900°C, sintering was predominant to the tensile strength. In the temperature from 900°C to 1200°C, the increase of strength became small by adding coke breeze in the nucleus pellet. It was presumed this result was caused by remarkable increase of void after coke combustion.
    In the sintering of raw material bed with embedded the coke breeze coating pellet, the surrounding temperature of pellet increased and the large void was generated below the pellet. Based on the 2-dimensional numeric evaluation, it was found the heat amounts of the pellet and gas heated by coke combustion were transported to the region under the pellet where the gas flow rate was low. It was considered this heat concentration caused the remarkable melting and large void formation.
  • DEM Simulation of Collapse Phenomena of Packed Bed of Raw Materials for Iron Ore Sinter during Charging

    pp. 1555-1560

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    DOI:10.2355/isijinternational.53.1555

    The collapse phenomena like an avalanche of sinter bed during charging of raw materials in the iron ore sintering are often observed. The collapse phenomena strongly influence the size segregation of raw materials in sinter bed, permeability and productivity of sinter. The reasons why collapse phenomena of the sinter bed during charging occur in the iron ore sintering have been discussed using the simulation by DEM (Discrete Element Method) in this work. As factors causing the collapse phenomena, there could be the granule shape of raw materials charged and the adhesion between the granules. First of all, a simulation model which is considered the adhesion force between the granules has been developed. The charging behavior of raw materials on the sintering machine was simulated by DEM. Effects of the adhesion force on deposition and collapse phenomena of the sinter bed were investigated. The deposition angle of the sinter bed obviously increases and the collapse phenomena of granules are clearly observed when the adhesion force was introduced into the granules. The ridges on the surface of the sinter bed which are feature of the collapse phenomena are confirmed. Therefore one of the reasons why the collapse phenomena occur during charging of the raw materials into the sintering machine would be adhesion of granules.
  • Sintering Behavior of Return Fines and their Effective Utilization Method

    pp. 1561-1570

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    DOI:10.2355/isijinternational.53.1561

    Return fines is unavoidably formed in sintering process, it recycles back into sintering and makes up 30 to 40% of the iron bearing materials. When deteriorated raw materials are applied, sintering process is balanced with higher ratio of return fines, which greatly affected sintering efficiency and fuel consumption.
    In order to reduce the return fines by effectively using, basic researches were conducted using modeled quasi-particles, consisting of return fines and sintering blend. Proper using ratio of two kinds of return fines were confirmed by measuring both granulating and bonding ability, then reasonable quasi-particle structure of return fines was proposed from the perspective of segregated basicity optimization. The results obtained were summarized as follows:
    Return fines generated from unassimilated iron ores, insufficient uniformity of melt, highly developed porous structure and lower internal force of eutectic structures. Assimilation ability and liquid fluidity of return fines were higher than sintering blend, resulting in promotion of low-temperature melt generation. The optimal addition of return fines from BF sieving was suggested not to surpass 30 mass% by melt generation balance, and the ratio for return fines from sintering sieving should be controlled at about 20 mass% with contradictory effect on bonding and granulation. Quasi-particles of returns fines were characterized by high compactness and uniformity at lower segregated basicity, weaken melt formation surrounding returns fines to strengthen that of iron ores was the effectively using way.
  • Influence of CaO Source on the Formation Behavior of Calcium Ferrite in Solid State

    pp. 1571-1579

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    DOI:10.2355/isijinternational.53.1571

    Calcium hydroxide and Calcium carbonate were used as CaO source to investigate the formation behavior of calcium ferrite in solid state below 1200°C. The density change of CaO–Fe2O3 samples with temperature were in-situ and off-line determined, with linear shrinkage rate test for mixed powders at a heating rate of 10°C/min and with Archimedes method for the pellets isothermal roasted at various temperatures and time, respectively. Phase composition of roasted samples was determined with X-ray powder diffraction method, and TG-DSC analysis was used to understand the decomposition behavior and formation of calcium ferrites in different heating rates. As a result, the formation of Ca2Fe2O5 could occur much earlier when calcium hydroxide was used as raw material; however, the formation rates of CaFe2O4 tend to be faster when calcium carbonate was used when the temperature is higher than 1100°C. In addition, the formation of Ca2Fe2O5 was supposed to be prior to CaFe2O4 in this study when the temperature is lower than 900°C.
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    2. Effect of Granule Structure on the Combustion Behavior of Coke Breeze for Iron Ore Sintering ISIJ International Vol.53(2013), No.9
    3. Utilization of Biomass for Iron Ore Sintering ISIJ International Vol.53(2013), No.9
  • Analysis of Combustion Rate of Various Carbon Materials for Iron Ore Sintering Process

    pp. 1580-1587

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    DOI:10.2355/isijinternational.53.1580

    The aim of this study was to relate the combustion rate of solid fuel for iron ore sintering process to its physical and chemical properties. In this study, we used 23 carbon materials including cokes, anthracites, charcoals, and so on. The physical and chemical properties of the carbon materials such as proximate and ultimate analysis, specific surface area, particle density, and porosity were evaluated. The combustion rates of the carbon materials were measured using thermobalance and fixed-bed combustion reactor. In the low temperature region, the combustion rates depended on the types of the carbon materials. This would be because the carbon structure and the volatile matter content affected the combustion rates significantly. In the high temperature region, on the other hand, the combustion rates were almost the same regardless of the types of the carbon materials.
  • Combustion Rate of Coke in Quasi-particle at Iron Ore Sintering Process

    pp. 1588-1593

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    DOI:10.2355/isijinternational.53.1588

    Temperature distribution in layer of the iron ore sintering process is one of the most important factors to decide the sinter quality. To estimate the temperature distribution in sinter layer needs knowledge of coke combustion rate. The purpose of this study is to clarify that coke combustion rate in the fine layer of the quasi-particle with considerations about void ratio and liquid formation. The following results were obtained. Interface chemical reaction rate constant, kc, was independent on the mixing ratio of coke. The higher mixing ratio of coke made the larger effective diffusion coefficient of oxygen, because the higher mixing ratio of coke made the higher void ratio in the sample after coke combustion. The coke combustion rate became small with increasing of liquid formation amount, because liquid phase in quasi-particle prevented oxygen diffusion in there.
  • Effect of Granule Structure on the Combustion Behavior of Coke Breeze for Iron Ore Sintering

    pp. 1594-1598

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    DOI:10.2355/isijinternational.53.1594

    In order to improve the coke combustion efficiency during iron ore sintering, the effect of coke granule structure was investigated with a TG-DTA and a new combination heating equipment capable of establishing similar heating pattern to the actual sintering bed. The results were analyzed as a function of granule type and neighboring specie as follows:
    The granule type was crucial to the combustion behavior of granules. On the other hand, the effect of neighbors was distinct over core coke particles; meanwhile, the effect remained uncertain in pellet type granules. The authors recommend composite type granules (fine coke particles adhering on a core particle) for the best choice. The type should bring 1.2% save of coke consumption and 2.3% increase in the heat front speed in comparison to coke particles of single type.
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    3. Influence of CaO Source on the Formation Behavior of Calcium Ferrite in Solid State ISIJ International Vol.53(2013), No.9
  • Utilization of Biomass for Iron Ore Sintering

    pp. 1599-1606

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    DOI:10.2355/isijinternational.53.1599

    Decrease of carbon dioxide emission is a serious subject in the steel works. Utilization of biomass as a carbon-neutral agent is an attractive one for iron ore sintering. Sinter pot tests were carried out with using raw biomass and biomass carbonized char. It is not good on yield and exhaust gas that raw biomass is used directly as carbon material for iron ore sintering. While, it is good on the productivity and the exhaust gas (NOx, SOx, dust, dioxins) that biomass carbonized char is used as carbon material. With using biomass char for the sintering, it is necessary to optimize operation (size control and moisture control of the biomass char), because combustion rate of the biomass char is too high. Biomass carbonized char is evaluated on sinter yield as similar as anthracite or coke. The biomass char is effective to decrease CO2, NOx, SOx, dust etc. emission in sinter exhaust gas.
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    3. Influence of CaO Source on the Formation Behavior of Calcium Ferrite in Solid State ISIJ International Vol.53(2013), No.9
  • Substitution of Charcoal for Coke Breeze in Iron Ore Sintering

    pp. 1607-1616

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    DOI:10.2355/isijinternational.53.1607

    The substitution of charcoal as an alternative fuel to coke breeze in a simulated Japanese Steel Mills (JSM) sinter blend was investigated. Compared with coke breeze, higher mix moisture contents were required for the sinter mixture containing charcoal to achieve optimum granulation. The green granules formed from the sinter mixture containing charcoal were clearly less dense and formed a less compacted green bed as evidenced by the packing density. To achieve return fines balance, fuel addition had to be increased from 3.62 to 4.17% (on a dry mixture basis) as the substitution of charcoal increased from 0 to 50%. However, at 100% subsitution, the sinter mixture failed to achieve balance even at a very high fuel addition level of 4.7%. Compared with the sinter fired with coke breeze, the sinter from the mixtures containing up to 50% charcoal was marginally weaker in terms of sinter yield, tumble strength (TI) and reduction disintegration (RDI). The reasons for weaker sinter are discussed. Fuel rate increased considerably with charcoal substitution due to increased fuel addition and decreased sinter yield. However, increasing fuel rate did not lead to a reduction of sintering productivity. In contrast, the sintering speed and productivity were maintained as the charcoal substitution rate increased from 0 to 25% and then increased considerably with further increase in charcoal substitution rate. The emission mechanisms of the CO, CO2, SO2 and NOX and H2O gases during sintering are clearly quite different. CO, CO2 and NOx emission was observed over the entire sintering process and varied slightly as the sintering process progressed. However, the SO2 and H2O emissions were observed only towards the completion of the sintering process. Both the CO and CO2 concentrations in the waste gas increased with the increasing substitution of charcoal for coke breeze; however the concentrations of SO2 and NOX in the waste gas decreased.
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  • Effect of Utilization of Metallic Fe Particles as an Agglomeration Agent on the Permeability of Sintering Bed

    pp. 1617-1624

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    DOI:10.2355/isijinternational.53.1617

    In this study, the effects of adding metallic Fe particles to coke in an effort to reduce the CO2 emissions associated with sintering were investigated. The changes to the structure and permeability of the sintering bed were analyzed in a laboratory-scale sintering simulator. The results were then used to compare agglomerates material containing metallic Fe particles with a 100% coke bed. The pressure drop of the packed bed of the mixture of model mini-pellets (ACPs) and coke particles increases until the bed reaches the temperature at which the adhering layer of ACP starts to melt, and then starts to gradually decrease. The pressure drop for metallic Fe particles, however, begins to decrease at an earlier stage, and then increases until its peak value. This difference can be attributed to differences in the products formed from oxidation.
    The sintering experiments were made by making changes to the CaO composition of the sintering bed: 5% to 15% was substituted with metallic Fe particles. A high CaO content resulted in a lower pressure drop of the bed from the start to 200 s sintering apparently due to the difference in the melting behavior of the materials at the initial stage of sintering.
  • Reduction of CO2 Emissions by Use of Pre-reduced Iron Ore as Sinter Raw Material

    pp. 1625-1632

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    DOI:10.2355/isijinternational.53.1625

    In order to reduce CO2 emissions at an ironmaking process, it is an effective measure to decrease a bonding agent rate at an iron ore sinter plant. In this study, effect of using a pre-reduced iron ore as a part of a sinter raw material on a sintering process was investigated mainly from a viewpoint of decreasing a bonding agent rate.
    Two brands of pisolitic iron ores were reduced up to wustite at 1173 K with reducing gas of which an oxidation degree was 55%. The pre-reduced iron ore was stable against reoxidation in the atmosphere and through a cyclic wet and dry treatment.
    Two brands of pisolitic iron ores and a Marra Mamba iron ore were pre-reduced and then used in a sinter pot test. A use of the pre-reduced iron ore was effective in decreasing a bonding agent rate at a given productivity. The reoxidation heat of the pre-reduced iron ore was estimated to be less than the combustion heat of the bonding agent being saved by use of the pre-reduced iron ore. The reoxidation heat is more effective in the sintering process than the combustion heat. The decrease of the bonding agent resulted in reduction of NOx emissions.
    A mass and heat balance shows that a use of a pre-reduced iron ore as a sinter raw material enables reduction of CO2 emissions not only at an ironmaking process but also at a whole integrated steel works.
  • Effect of Oxygen Enrichment on Sintering with Combined Usage of Coke Breeze and Gaseous Fuel

    pp. 1633-1641

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    DOI:10.2355/isijinternational.53.1633

    The temperature in the sintering bed is preferably maintained between 1200°C and 1400°C during sintering to produce high strength and reducibility sintered ore. To achieve this condition, the technology of combined usage of coke breeze and gaseous fuel, which is fed properly from the top surface of the sintering bed, was developed. In this paper, the effect of oxygen enrichment with combined usage of coke breeze and gaseous fuel on the heat pattern in sintering bed and cold strength of sintered ore was investigated. The cold strength of sintered ore was improved by the oxygen enrichment in the pot test. Then, the holding time over 1200°C during sintering was extended and improvement of strength would be attributed to promotion of the sintering reaction. By the simulation model calculations based on chemical kinetics, it is considered that the further extension of the holding time over 1200°C due to oxygen enrichment is caused of an increase in the distance between the combustion points of the coke breeze and gaseous fuel. However, improvement of the cold strength reached saturation over 32 vol.% of the oxygen concentration in suction air. It is also considered that the excessive increase of the distance between the combustion points of coke breeze and gaseous fuel decreases overlap of respective heat transfer and doesn’t contribute to the expansion of holding time over 1200°C.
  • Effect of Coke Combustion Rate Equation on Numerical Simulation of Temperature Distribution in Iron Ore Sintering Process

    pp. 1642-1647

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    DOI:10.2355/isijinternational.53.1642

    It is thought that numerical simulation model for estimation of temperature distribution in the iron ore sintering process is useful tool for stable operation of this process. The purpose of this study is to develop new numerical simulation model based on a combination of Hottel’s equation and coke combustion rate equation in quasi-particle derived from previous study. The following results were obtained. More practical temperature distribution could be calculated using coke combustion rate from previous work than in case of using only Hottel’s equation. Decrease of temperature distribution in the sintering layer was found with consideration of the liquid phase formation effect on coke combustion rate. This effect will increase with increasing of fine coke amount in the process.
  • Simulation of Sintering Process – Effects of Contraction Force by Particle Shrinkage and Melted Particle Volume on Growth of Void and Crack –

    pp. 1648-1657

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    DOI:10.2355/isijinternational.53.1648

    The particle and the air motions in the nearly full scale sintering bed have been simulated to elucidate the void (crack) formation mechanism and the crack growth mechanism. The simulation results showed that the contraction force produced the large scale cracks in the wide area in the fixation zone above the melting zone. Since the contraction force acts toward the particle center from each contact point, the resultant force in the inhomogeneous configuration of contact point moves the particles in the melted liquid. This migration produced the agglomerate which grew continuously. The bed weight in the sintering particle bed disrupted the large agglomerate. Through the process the cracks (voids) further grew and merged to a large scale crack. Large scale cracks developed taking account of the contraction force well represented the measured large scale cracks in the full scale sintering bed obtained using CT scan. In the case that the liquid volume produced by melting was large such as 88% of particle volume, the distance between the neighboring particles in the melted liquid became large and the liquid film between particles became thick. Thus it became hard for particle to move by the resistance force in the liquid. Therefore the agglomerate and the void did not grow to the large scale crack. The agglomeration of particles for 88% of particle volume melted was not so fast that the sintering bed in which the agglomerate particles uniformly distributed was formed.
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  • Non-linear State Estimator for the On-line Control of a Sinter Plant

    pp. 1658-1664

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    DOI:10.2355/isijinternational.53.1658

    This is a thermal control model that aims to increase sinter process stability and standardize control criteria using the position and temperature of the sintering point or BTP calculated by the model. The process computer sends to the instrumentation setpoints of return fines, strand speed and coke content. The model was successfully tested at the facilities of AM Asturias with contrasted improvements in productivity, cok consumption and quality stability.
  • Efficient and Clean Production Practice of Large-Scale Sintering Machine

    pp. 1665-1672

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    DOI:10.2355/isijinternational.53.1665

    Shougang Jingtang Iron and Steel plant has built the new generation sinter plant with two 500 m2 sintering machines at Caofeidian Port, the thought of Metallurgical Process Engineering was led into, and the ordering, coordinated, efficient, continuous production of sinter manufacturing processes were achieved. Whose overall design adopted advanced, proven process technology and large-scale equipments, which broke through long flow layout in traditional metallurgical projects and achieved short flow with compact arrangement. Widening side plate of sintering machine and annular cooler were used to create conditions for increasing production capacity, lowering energy consumption of unit production. According to the concept of recycling economy and energy saving, the high-temperature exhaust heat of annular cooler was recycled, the iron and carbon waste and waste water were dissolved, which gained sinter production energy conversion, by applying dense phase pneumatic dust conveying technology, the secondary pollution of dust was avoided, the concentration of SO2 emission was below 47 mg/Nm3 in the flue gas. Through adopting deep bed sintering, since producing in May 2009, the equipments ran smoothly with sintering bed depth reached 860 mm in sintering production, qualification rate of sinter ores reached 99.71%, drum index was 81.79%, and the energy consumption of process was 47.70 kgce/t, which attained first class domestically and internationally advanced level.
  • Optimization of Firing Temperature for Hematite Pellets

    pp. 1673-1682

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    DOI:10.2355/isijinternational.53.1673

    The heat hardening by oxidation is a process commonly used in iron ore pelletization process. The green pellets are fired in induration machine using Corex gas at JSW Steel Limited Pellet Plant. The firing temperature of induration machine strongly influences the physical and metallurgical properties of the pellet. Due to absence of exothermic reaction and poor roasting property of hematite pellet, the energy consumption of hematite pellet production is at higher side and requires higher roasting temperature. In present pelletization process, carbon burdened method is found to be more favorable technique in practice to enhance the induration of hematite pellets. Coke breeze is added in the pellet mix at JSW pellet plants to get the inherent fuel value of a hematite green ball equal to that of a magnetite pelletizing feed. The firing temperature (from corex gas) of the induration machine and carbon addition in the pellet mix is interrelated and decides physical and metallurgical properties of the pellets. At JSW Steel Pellet Plant the carbon addition varies from 0.90 to 1.50% and firing temperature varies from 1230 to 1320°C. Fluctuations in physical and metallurgical properties were observed due to deviation in carbon addition and firing temperature. Optimization of external firing temperature and coke breeze addition in the green pellet mix is necessary to get the desired properties of the pellet for iron making units. Basket trials were carried out at pellet plant induration machine by varying the external firing temperature from 1220 to 1330°C and coke breeze addition from 0.7 to 1.4%. At firing temperature of 1220, 1250, 1280, 1310 and 1330°C the optimum carbon addition 1.30, 1.20, 1.10, 0.90 and 0.70% achieved the optimum physical and metallurgical properties of the pellet for iron making units respectively.

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